Beam selection for uplink and downlink based mobility

ABSTRACT

Aspects of the present disclosure provide methods and apparatus for beam selection in uplink-based and downlink-based mobility scenarios, for example, for new radio (NR) systems which can improve handover reliability, reduce handover frequency, and improve power efficiency. Certain aspects provide a method for wireless communications by a user equipment (UE). The method generally includes transmitting an uplink reference signal with an indication of a preferred downlink beam and receiving a downlink transmission based, at least in part, on the uplink reference signal.

CROSS-REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM

This application claims benefit of and priority to U.S. ProvisionalPatent Application Ser. No. 62/293,761, filed Feb. 10, 2016, which isherein incorporated by reference in its entirety for all applicablepurposes.

TECHNICAL FIELD

The present disclosure generally relates to wireless communications and,more particularly, to methods and apparatus for beam selection inuplink-based and downlink-based mobility scenarios, for example, for newradio (NR) systems which can improve handover reliability, reducehandover frequency, and improve power efficiency.

INTRODUCTION

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency divisional multiple access (SC-FDMA) systems,and time division synchronous code division multiple access (TD-SCDMA)systems.

A wireless communication network may include a number of base stations(BS) that can support communication for a number of user equipments(UEs). A UE may communicate with a BS via downlink and uplink. Thedownlink (or forward link) refers to the communication link from the BSto the UE, and the uplink (or reverse link) refers to the communicationlink from the UE to the BS. As will be described in more detail herein,a BS may be referred to as a Node B, gNB, access point (AP), radio head,transmission reception point (TRP), new radio (NR) BS, 5G Node B, etc.).

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is new radio (NR), for example, 5G radioaccess. NR is a set of enhancements to the LTE mobile standardpromulgated by Third Generation Partnership Project (3GPP). It isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingOFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink(UL) as well as support beamforming, multiple-input multiple-output(MIMO) antenna technology, and carrier aggregation. However, as thedemand for mobile broadband access continues to increase, there exists aneed for further improvements in NR technology. Preferably, theseimprovements should be applicable to other multi-access technologies andthe telecommunication standards that employ these technologies.

Some wireless communication standards base user equipment handoffdecisions based, at least in part, on downlink measurements. Futuregeneration wireless communication may focus on user-centric networks.Accordingly, apparatus, methods, processing systems, and computerprogram products for new radio (NR) (new radio access technology or 5Gtechnology) are desirable.

BRIEF SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedcommunications between access points and stations in a wireless network.

Certain aspects of the present disclosure generally relate to methodsand apparatus for beam selection in uplink-based and downlink-basedmobility scenarios. For example, a downlink beam used for downlinksignaling and/or a handover command (and selected transmission point) bya base station (BS) can be based on measurement of an uplink referencesignal from the user equipment (UE) and/or based on an indication in theuplink reference signal of a preferred beam and/or transmission point.

Certain aspects of the present disclosure provide a method for wirelesscommunication by a UE. The method generally includes transmitting anuplink reference signal with an indication of a preferred downlink beamand receiving a downlink transmission based, at least in part, on theuplink reference signal.

Certain aspects of the present disclosure provide an apparatus forwireless communication by a UE. The apparatus generally includes meansfor transmitting an uplink reference signal with an indication of apreferred downlink beam and means for receiving a downlink transmissionbased, at least in part, on the uplink reference signal.

Certain aspects of the present disclosure provide an apparatus forwireless communication by a UE. The apparatus generally includes atleast one processor and a memory coupled with the at least oneprocessor. The at least one processor is generally configured totransmit an uplink reference signal with an indication of a preferreddownlink beam and receive a downlink transmission based, at least inpart, on the uplink reference signal.

Certain aspects of the present disclosure provide a computer readablemedium storing computer executable code for causing a UE to transmit anuplink reference signal with an indication of a preferred downlink beamand receive a downlink transmission based, at least in part, on theuplink reference signal.

Certain aspects of the present disclosure provide a method for wirelesscommunication by a BS. The method generally includes receiving, from aUE, an uplink reference signal with an indication of a preferreddownlink beam and transmitting a downlink transmission to the UE based,at least in part, on the uplink reference signal.

Certain aspects of the present disclosure provide an apparatus forwireless communication by a BS. The apparatus generally includes meansfor receiving, from a UE, an uplink reference signal with an indicationof a preferred downlink beam and means for transmitting a downlinktransmission to the UE based, at least in part, on the uplink referencesignal.

Certain aspects of the present disclosure provide an apparatus forwireless communication by a BS. The apparatus generally includes atleast one processor and a memory coupled with the at least oneprocessor. The at least one processor is generally configured toreceive, from a UE, an uplink reference signal with an indication of apreferred downlink beam and transmit a downlink transmission to the UEbased, at least in part, on the uplink reference signal.

Certain aspects of the present disclosure provide a computer readablemedium storing computer executable code for causing a BS to receive,from a UE, an uplink reference signal with an indication of a preferreddownlink beam and transmit a downlink transmission to the UE based, atleast in part, on the uplink reference signal.

Aspects generally include methods, apparatus, systems, computer programproducts, and processing systems, as substantially described herein withreference to and as illustrated by the accompanying drawings.

Other aspects, features, and embodiments of the present invention willbecome apparent to those of ordinary skill in the art, upon reviewingthe following description of specific, exemplary embodiments of thepresent invention in conjunction with the accompanying figures. Whilefeatures of the present invention may be discussed relative to certainembodiments and figures below, all embodiments of the present inventioncan include one or more of the advantageous features discussed herein.In other words, while one or more embodiments may be discussed as havingcertain advantageous features, one or more of such features may also beused in accordance with the various embodiments of the inventiondiscussed herein. In similar fashion, while exemplary embodiments may bediscussed below as device, system, or method embodiments it should beunderstood that such exemplary embodiments can be implemented in variousdevices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. The appended drawingsillustrate only certain typical aspects of this disclosure, however, andare therefore not to be considered limiting of its scope, for thedescription may admit to other equally effective aspects.

FIG. 1 illustrates an exemplary deployment in which multiple wirelessnetworks have overlapping coverage, in accordance with certain aspectsof the disclosure.

FIG. 2 is a diagram illustrating an example of an access network, inaccordance with certain aspects of the disclosure.

FIG. 3 is a diagram illustrating an example of a DL frame structure in atelecommunications system, in accordance with certain aspects of thedisclosure.

FIG. 4 is a diagram illustrating an example of an UL frame structure ina telecommunications system, in accordance with certain aspects of thedisclosure.

FIG. 5 is a diagram illustrating an example of radio protocolarchitecture for the user and control plane, in accordance with certainaspects of the disclosure.

FIG. 6 is a diagram illustrating an example of a base station (BS) anduser equipment (UE) in an access network, in accordance with certainaspects of the disclosure.

FIG. 7 illustrates an example logical architecture of a distributedradio access network (RAN), in accordance with certain aspects of thepresent disclosure.

FIG. 8 illustrates an example physical architecture of a distributedRAN, in accordance with certain aspects of the present disclosure.

FIG. 9 is a diagram illustrating an example of a downlink (DL)-centricsubframe, in accordance with certain aspects of the present disclosure.

FIG. 10 is a diagram illustrating an example of an uplink (UL)-centricsubframe, in accordance with certain aspects of the present disclosure.

FIG. 11 is a call-flow diagram illustrating an example downlink-basedhandover procedure, in accordance with certain aspects of thedisclosure.

FIG. 12 is a call-flow diagram illustrating an example uplink-basedhandover procedure, in accordance with certain aspects of thedisclosure.

FIG. 13 is a call flow illustrating example operations, performed by aUE, for uplink-based mobility, in accordance with certain aspects of thedisclosure.

FIG. 14 is a call flow illustrating example operations, performed by asource or target BS, for uplink-based mobility, in accordance withcertain aspects of the disclosure.

FIG. 15 illustrates an example state diagram showing example UE-centricuplink-based mobility, in accordance with certain aspects of thedisclosure.

FIG. 16 is call flow diagram illustrating beam selection foruplink-based mobility, in accordance with aspects of the presentdisclosure.

FIG. 17 illustrates example operations, performed by a UE, for beamselection for downlink-mobility, in accordance with certain aspects ofthe disclosure.

FIG. 18 illustrates example operations, performed by a BS, for beamselection for downlink-based mobility, in accordance with certainaspects of the disclosure.

FIG. 19 illustrates an example call flow diagram for beam selection,during an initial access procedure, for downlink-based mobility, inaccordance with certain aspects of the disclosure.

FIG. 20 illustrates an example call flow diagram for beam selection,after an initial access procedure, for downlink-based mobility, inaccordance with certain aspects of the disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer program products for new radio (NR) (new radioaccess technology or 5G technology).

Aspects of the present disclosure provide techniques and apparatus forperforming a straight-forward, quick, and resource-efficient handoverprocedure. As described herein, for uplink-based mobility, handovers maybe performed based, at least in part, on uplink signal measurementstaken by base stations (e.g., Node Bs (NBs), gNBs, access points (APs),smart radio heads (SRHs), transmission reception points (TRPs), NR BSs,5G NBs, etc.), while for downlink-based mobility, handovers may beperformed based on measurements taken by UEs. For example, 5G and otherfuture communications systems may focus on creating a more user-centricnetwork.

Aspects of the present disclosure provide a framework for (forward andbackward) handover based on uplink and/or downlink measurements. Inaddition, 5G and other telecommunications may use beamformedtransmissions. Aspects of the present disclosure also provide for beamselection techniques for both uplink-based and downlink-based mobilityscenarios.

In downlink-based mobility, a UE may receive reference signals (e.g.,measurement reference signals (MRS) from a BS and report measurements tothe BS. The UE can also report a preferred beam and/or a preferredtransmission point. The indication of the preferred beam and/ortransmission point may be included in an uplink reference signal fromthe UE. Mobility decisions (e.g., for a handover command) at the BS canbe based on measurement of the uplink reference signal and/or based onthe indication in the uplink reference signal of the preferred beamand/or transmission point. The BS can also use the indication of thepreferred beam for beamforming downlink signals to the UE.

In uplink-based mobility, a BS may make mobility decisions based onmeasurements of an uplink reference signal from a UE (e.g., withoutsending any MRS). The BS can also make the beam selection and/ortransmission point selection.

In a hybrid mobility scheme, a BS can make mobility decisions and beamselection decisions based on reference signal parameters, for example,similar to the uplink-based mobility. In addition, the BS can alsotransmit MRSs and can refine the mobility decision and/or beam selectionbased on feedback from a UE (e.g., in the uplink reference signals).

Advantageously, a UE may receive a configuration for an uplink referencesignal from a serving BS. A non-serving BS (e.g., a target BS) mayreceive a configuration for the uplink reference signal from the servingBS. In this manner, the UE may transmit the uplink reference signalwhich the target BS may receive. As described herein, either the sourceor target BS may transmit a handover command and/or connectionreconfiguration message based, at least in part, on measurements of thereceived uplink reference signal.

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects. Yes in some scenarios, the example can be preferred.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well-known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using hardware,software/firmware, or combinations thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One non-limiting example of theprocessors is the Snapdragon processor. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software/firmware, middleware, microcode,hardware description language, or otherwise.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software/firmware, orcombinations thereof. If implemented in software, the functions may bestored or transmitted over as one or more instructions or code on acomputer-readable medium. Software shall be construed broadly to meaninstructions, data, or any combination thereof, whether referred to assoftware, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. Computer-readable media include both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another.The processor may be responsible for managing the bus and generalprocessing, including the execution of software modules stored on themachine-readable storage media.

A computer-readable storage medium may be coupled to a processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product and/orcomputer readable medium for performing the operations presented herein.For example, such a computer program product may comprise acomputer-readable medium having instructions stored (and/or encoded)thereon, the instructions being executable by one or more processors toperform the operations described herein.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

The techniques described herein may be used for various wirelesscommunication networks such as code division multiple access (CDMA),time division multiple access (TDMA), frequency division multiple access(FDMA), orthogonal FDMA (OFDMA), single carrier FDMA (SC-FDMA) and othernetworks. The terms “network” and “system”” are often usedinterchangeably. A CDMA network may implement a radio access technology(RAT) such as universal terrestrial radio access (UTRA), cdma2000, etc.UTRA includes wideband CDMA (WCDMA) and other variants of CDMA. cdma2000covers IS-2000, IS-95 and IS-856 standards. IS-2000 is also referred toas 1× radio transmission technology (1×RTT), CDMA2000 1×, etc. A TDMAnetwork may implement a RAT such as global system for mobilecommunications (GSM), enhanced data rates for GSM evolution (EDGE), orGSM/EDGE radio access network (GERAN). An OFDMA network may implement aRAT such as evolved UTRA (E-UTRA), ultra mobile broadband (UMB), IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRAand E-UTRA are part of universal mobile telecommunication system (UMTS).3GPP long-term evolution (LTE) and LTE-Advanced (LTE-A) are releases ofUMTS that use E-UTRA, which employs OFDMA on the downlink and SC-FDMA onthe uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andRATs mentioned above as well as other wireless networks and RATs.

It is noted that while aspects may be described herein using terminologycommonly associated with 3G and/or 4G wireless technologies, aspects ofthe present disclosure can be applied in other generation-basedcommunication systems, such as 5G and later, including NR technologies.

An Example Wireless Communication System

FIG. 1 illustrates an example deployment in which aspects of the presentdisclosure may be implemented. For example, a user equipment (UE) 110transmits an uplink reference signal to a base station (BS) 122 (e.g., agNB, a transmission reception point (TRP), Node B (NB), 5G NB, accesspoint (AP), new radio (NR) BS, etc.). The uplink reference signal caninclude an indication of a preferred downlink beam. The UE 110 canreceive a downlink from the BS 122 based, at least in part, on theuplink reference signal. For downlink-based mobility, the UE 110 mayreceive measurement reference signals (MRS) transmitted with differentbeams from the BS 122. The UE 110 can select the preferred beam based onthe MRS. The BS 122 can beamform the downlink signal to the UE using thepreferred beam and/or the BS 122 can send a handover command to the UE110 based, at least in part, on the uplink reference signal. Foruplink-based mobility the UE 110 sends the uplink reference signal,without MRS from the BS 122, and the BS 122 can perform beam selectionand/or handover decisions based on measurement of the uplink referencesignal. In some cases a non-serving BS can receive the uplink referencesignals and send a handover command to the UE 110.

FIG. 1 shows an exemplary deployment in which multiple wireless networkshave overlapping coverage. The system illustrated in FIG. 1 may include,for example, an evolved universal terrestrial radio access network(E-UTRAN) 120 may support long term evolution (LTE) and a GMS network130. According to aspects, the system illustrated in FIG. 1 may includeone or more other networks, such as a NR network. The radio accessnetwork may include a number of s 122 BSs and other network entitiesthat can support wireless communication for UEs. In some cases, a NRnetwork may include a central unit (CU) and distributed units (DUs).

Each BS may provide communication coverage for a particular geographicarea. The term “cell” can refer to a coverage area of a BS or BSsubsystem serving this coverage area. A serving gateway (S-GW) 124 maycommunicate with E-UTRAN 120 and may perform various functions such aspacket routing and forwarding, mobility anchoring, packet buffering,initiation of network-triggered services, etc. A mobility managemententity (MME) 126 may communicate with E-UTRAN 120 and serving gateway124 and may perform various functions such as mobility management,bearer management, distribution of paging messages, security control,authentication, gateway selection, etc. The network entities in LTE aredescribed in 3GPP TS 36.300, entitled “Evolved Universal TerrestrialRadio Access (E-UTRA) and Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN); Overall description,” which is publicly available.

In NR systems, the term “cell” and gNB, Node B, 5G NB, or TRP may beinterchangeable. In some examples, a cell may not necessarily bestationary, and the geographic area of the cell may move according tothe location of a mobile base station. In some examples, the basestations may be interconnected to one another and/or to one or moreother base stations or network nodes (not shown) in the access network100 through various types of backhaul interfaces such as a directphysical connection, a virtual network, or the like using any suitabletransport network.

A radio access network (RAN) 130 may support GSM and may include anumber of base stations 132 and other network entities that can supportwireless communication for UEs. A mobile switching center (MSC) 134 maycommunicate with the RAN 130 and may support voice services, providerouting for circuit-switched calls, and perform mobility management forUEs located within the area served by MSC 134. Optionally, aninter-working function (IWF) 140 may facilitate communication betweenMME 126 and MSC 134 (e.g., for 1×CSFB).

E-UTRAN 120, serving gateway 124, and MME 126 may be part of an LTEnetwork 102. RAN 130 and MSC 134 may be part of a GSM network 104. Forsimplicity, FIG. 1 shows only some network entities in the LTE network102 and the GSM network 104. The LTE and GSM networks may also includeother network entities that may support various functions and services.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular RAT andmay operate on one or more frequencies. A RAT may also be referred to asa radio technology, an air interface, etc. A frequency may also bereferred to as a carrier, a frequency channel, etc. Each frequency maysupport a single RAT in a given geographic area in order to avoidinterference between wireless networks of different RATs. In some cases,NR or 5G RAT networks may be deployed.

A UE 110 may be stationary or mobile and may also be referred to as amobile station, a terminal, an access terminal, a subscriber unit, astation, etc. A UE may also be referred to as an access terminal, aterminal, a mobile station, a subscriber unit, a station, etc. A UE maybe a Customer Premises Equipment (CPE), a cellular phone (e.g., a smartphone), a personal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a laptop computer, a cordlessphone, a wireless local loop (WLL) station, a tablet, a camera, a gamingdevice, a netbook, a smartbook, an ultrabook, medical device orequipment, biometric sensors/devices, mammal implant device, wearabledevices (smart watches, smart clothing, smart glasses, smart wristbands, smart jewelry (e.g., smart ring, smart bracelet)), anentertainment device (e.g., a music or video device, or a satelliteradio), a vehicular component or sensor, smart meters/sensors,industrial manufacturing equipment, military firearm or communicationdevice, a global positioning system device, or any other suitable devicethat is configured to communicate via a wireless or wired medium. SomeUEs may be considered evolved or enhanced machine-type communication(eMTC) UEs. MTC and eMTC UEs include, for example, robots, drones,remote devices, such as sensors, meters, monitors, location tags, etc.,that may communicate with a base station, another device (e.g., remotedevice), or some other entity. A wireless node may provide, for example,connectivity for or to a network (e.g., a wide area network such asInternet or a cellular network) via a wired or wireless communicationlink. Some UEs may be considered Internet-of-Things (IoT) devices.

Upon power up, UE 110 may search for wireless networks from which it canreceive communication services. If more than one wireless network isdetected, then a wireless network with the highest priority may beselected to serve UE 110 and may be referred to as the serving network.UE 110 may perform registration with the serving network, if necessary.UE 110 may then operate in a connected mode to actively communicate withthe serving network. Alternatively, UE 110 may operate in an idle modeand camp on the serving network if active communication is not requiredby UE 110.

UE 110 may be located within the coverage of cells of multiplefrequencies and/or multiple RATs while in the idle mode. For LTE, UE 110may select a frequency and a RAT to camp on based on a priority list.This priority list may include a set of frequencies, a RAT associatedwith each frequency, and a priority of each frequency. For example, thepriority list may include three frequencies X, Y and Z. Frequency X maybe used for LTE and may have the highest priority, frequency Y may beused for GSM and may have the lowest priority, and frequency Z may alsobe used for GSM and may have medium priority. In general, the prioritylist may include any number of frequencies for any set of RATs and maybe specific for the UE location. UE 110 may be configured to prefer LTE,when available, by defining the priority list with LTE frequencies atthe highest priority and with frequencies for other RATs at lowerpriorities, e.g., as given by the example above.

UE 110 may operate in the idle mode as follows. UE 110 may identify allfrequencies/RATs on which it is able to find a “suitable” cell in anormal scenario or an “acceptable” cell in an emergency scenario, where“suitable” and “acceptable” are specified a standard (e.g., LTE). UE 110may then camp on the frequency/RAT with the highest priority among allidentified frequencies/RATs. UE 110 may remain camped on thisfrequency/RAT until either (i) the frequency/RAT is no longer availableat a predetermined threshold or (ii) another frequency/RAT with a higherpriority reaches this threshold. This operating behavior for UE 110 inthe idle mode is described in 3GPP TS 36.304, entitled “EvolvedUniversal Terrestrial Radio Access (E-UTRA); User Equipment (UE)procedures in idle mode,” which is publicly available.

UE 110 may be able to receive packet-switched (PS) data services fromLTE network 102 and may camp on the LTE network while in the idle mode.LTE network 102 may have limited or no support for voice-over-Internetprotocol (VoIP), which may often be the case for early deployments ofLTE networks. Due to the limited VoIP support, UE 110 may be transferredto another wireless network of another RAT for voice calls. Thistransfer may be referred to as circuit-switched (CS) fallback. UE 110may be transferred to a RAT that can support voice service such as1×RTT, WCDMA, GSM, etc. For call origination with CS fallback, UE 110may initially become connected to a wireless network of a source RAT(e.g., LTE) that may not support voice service. The UE may originate avoice call with this wireless network and may be transferred throughhigher-layer signaling to another wireless network of a target RAT thatcan support the voice call. The higher-layer signaling to transfer theUE to the target RAT may be for various procedures, e.g., connectionrelease with redirection, PS handover, etc.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a base station) can allocate resources forcommunication among some or all devices and equipment within its servicearea or cell. Within the present disclosure, as discussed further below,the scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity.

Base stations are not the only entities that may function as ascheduling entity. That is, in some examples, a UE may function as ascheduling entity, scheduling resources for one or more subordinateentities (e.g., one or more other UEs). In this example, the UE isfunctioning as a scheduling entity, and other UEs utilize resourcesscheduled by the UE for wireless communication. A UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may optionally communicatedirectly with one another in addition to communicating with thescheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

FIG. 2 is a diagram illustrating an example of an access network 200. UE206 may transmit an uplink reference signal which may be received byboth a serving and non-serving BSs 204, 208. Serving and non-serving BSs204, 208 may receive the uplink reference signal and either of the BSsmay transmit a handover command to the UE based, at least in part, onthe uplink reference signal. The uplink reference signal can include anindication of a preferred downlink beam. For downlink-based mobility,the UE 206 may receive measurement reference signals (MRS) transmittedwith different beams from the BS 204. The UE 206 can select thepreferred beam based on the MRS. The BS 204 can beamform the downlinksignal to the UE using the preferred beam and/or the BS 204 can send ahandover command to the UE 206 based, at least in part, on the uplinkreference signal. For uplink-based mobility the UE 206 sends the uplinkreference signal, without MRS from the BS 204, and the BS 204 canperform beam selection and/or handover decisions based on measurement ofthe uplink reference signal. In some cases a non-serving BS 208 canreceive the uplink reference signals and send a handover command to theUE 206.

In FIG. 2, the access network 200 is divided into a number of cellularregions (cells) 202. One or more lower power class BS 208 may havecellular regions 210 that overlap with one or more of the cells 202. Alower power class BS 208 may be referred to as a remote radio head(RRH). The lower power class BS 208 may be a femto cell (e.g., home NB(HNB)), pico cell, or micro cell. The macro NBs 204 are each assigned toa respective cell 202 and are configured to provide an access point tothe EPC 110 for all the UEs 206 in the cells 202. There is nocentralized controller in this example of an access network 200, but acentralized controller may be used in alternative configurations. TheBSs 204 are responsible for all radio related functions including radiobearer control, admission control, mobility control, scheduling,security, and connectivity to the serving gateway 124.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplexing (FDD) andtime division duplexing (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employingOFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents fromthe 3GPP organization. CDMA2000 and UMB are described in documents fromthe 3GPP2 organization. The actual wireless communication standard andthe multiple access technology employed will depend on the specificapplication, the overall design constraints imposed on the system, ordesired operating parameters.

The BS 204 may have multiple antennas supporting MIMO technology (e.g.,massive MIMO). The use of MIMO technology enables the BS 204 to exploitthe spatial domain to support spatial multiplexing, beamforming, andtransmit diversity. Spatial multiplexing may be used to transmitdifferent streams of data simultaneously on the same frequency. The datastreams may be transmitted to a single UE 206 to increase the data rateor to multiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (e.g., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on the DL.The spatially precoded data streams arrive at the UE(s) 206 withdifferent spatial signatures, which enables each of the UE(s) 206 torecover the one or more data streams destined for that UE 206. On theUL, each UE 206 transmits a spatially precoded data stream, whichenables the BS 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM on the DL. OFDM is a spread-spectrum technique that modulates dataover a number of subcarriers within an OFDM symbol. The subcarriers arespaced apart at precise frequencies. The spacing provides“orthogonality” that enables a receiver to recover the data from thesubcarriers. In the time domain, a guard interval (e.g., cyclic prefix)may be added to each OFDM symbol to combat inter-OFDM-symbolinterference. The UL may use SC-FDMA in the form of a DFT-spread OFDMsignal to compensate for high peak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein a telecommunications system (e.g., LTE). A frame (10 ms) may bedivided into 10 equally sized sub-frames with indices of 0 through 9.Each sub-frame may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource block. The resource grid is divided into multiple resourceelements. In LTE, a resource block contains 12 consecutive subcarriersin the frequency domain and, for a normal cyclic prefix in each OFDMsymbol, 7 consecutive OFDM symbols in the time domain, or 84 resourceelements. For an extended cyclic prefix, a resource block contains 6consecutive OFDM symbols in the time domain and has 72 resourceelements. Some of the resource elements, as indicated as R 302, 304,include DL reference signals (DL-RS). The DL-RS include Cell-specific RS(CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS)304. UE-RS 304 are transmitted only on the resource blocks upon whichthe corresponding physical DL shared channel (PDSCH) is mapped. Thenumber of bits carried by each resource element depends on themodulation scheme. Thus, the more resource blocks that a UE receives andthe higher the modulation scheme, the higher the data rate for the UE.

In LTE, a NB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the BS. Theprimary and secondary synchronization signals may be sent in symbolperiods 6 and 5, respectively, in each of subframes 0 and 5 of eachradio frame with the normal cyclic prefix (CP). The synchronizationsignals may be used by UEs for cell detection and acquisition. The NBmay send a Physical Broadcast Channel (PBCH) in symbol periods 0 to 3 inslot 1 of subframe 0. The PBCH may carry certain system information.

The NB may send a Physical Control Format Indicator Channel (PCFICH) inthe first symbol period of each subframe. The PCFICH may convey thenumber of symbol periods (M) used for control channels, where M may beequal to 1, 2 or 3 and may change from subframe to subframe. M may alsobe equal to 4 for a small system bandwidth, e.g., with less than 10resource blocks. The NB may send a Physical HARQ Indicator Channel(PHICH) and a Physical Downlink Control Channel (PDCCH) in the first Msymbol periods of each subframe. The PHICH may carry information tosupport hybrid automatic repeat request (HARQ). The PDCCH may carryinformation on resource allocation for UEs and control information fordownlink channels. The NB may send a Physical Downlink Shared Channel(PDSCH) in the remaining symbol periods of each subframe. The PDSCH maycarry data for UEs scheduled for data transmission on the downlink.

The NB may send the PSS, SSS, and PBCH in the center 1.08 MHz of thesystem bandwidth used by the NB. The NB may send the PCFICH and PHICHacross the entire system bandwidth in each symbol period in which thesechannels are sent. The NB may send the PDCCH to groups of UEs in certainportions of the system bandwidth. The NB may send the PDSCH to specificUEs in specific portions of the system bandwidth. The NB may send thePSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to all UEs, maysend the PDCCH in a unicast manner to specific UEs, and may also sendthe PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element (RE) may cover one subcarrier in one symbol periodand may be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1, and 2. ThePDCCH may occupy 9, 18, 36, or 72 REGs, which may be selected from theavailable REGs, in the first M symbol periods, for example. Only certaincombinations of REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. A NB may send the PDCCH to the UE in any ofthe combinations that the UE will search.

In other systems (e.g., such NR or 5G systems), a Node B may transmitthese or other signals in these locations or in different locations ofthe subframe.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein a telecommunications system (e.g., LTE). The available resourceblocks for the UL may be partitioned into a data section and a controlsection. The control section may be formed at the two edges of thesystem bandwidth and may have a configurable size. The resource blocksin the control section may be assigned to UEs for transmission ofcontrol information. The data section may include all resource blocksnot included in the control section. The UL frame structure results inthe data section including contiguous subcarriers, which may allow asingle UE to be assigned all of the contiguous subcarriers in the datasection.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to a BS. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theBS. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve UL synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany UL data/signaling. Each random access preamble occupies a bandwidthcorresponding to six consecutive resource blocks. The starting frequencyis specified by the network. That is, the transmission of the randomaccess preamble is restricted to certain time and frequency resources.There is no frequency hopping for the PRACH. The PRACH attempt iscarried in a single subframe (1 ms) or in a sequence of few contiguoussubframes and a UE can make only a single PRACH attempt per frame (10ms).

As will described in more detail below, in other systems (e.g., NR or 5Gsystems), different uplink and/or downlink frame structures may be used.

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in a telecommunicationssystem (e.g., LTE). The radio protocol architecture for the UE and theBS is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1(L1 layer) is the lowest layer and implements various physical layersignal processing functions. The L1 layer will be referred to herein asthe physical layer 506. Layer 2 (L2 layer) 508 is above the physicallayer 506 and is responsible for the link between the UE and BS over thephysical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the BS on the network side. Although not shown, the UE mayhave several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between BSs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and BSis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the BS andthe UE.

FIG. 6 is a block diagram of a BS 610 in communication with a UE 650 inan access network in accordance with aspects of the present disclosure.The BSs of FIG. 1 and FIG. 2 may include one or more components of BS610 illustrated in FIG. 6. Similarly, the UEs illustrated in FIGS. 1 and2 may include one or more components of UE 650 as illustrated in FIG. 6.One or more components of the UE 650 and BS 610 may be configured toperform the operations described herein.

In the DL, upper layer packets from the core network are provided to acontroller/processor 675. The controller/processor 675 implements thefunctionality of the L2 layer. In the DL, the controller/processor 675provides header compression, ciphering, packet segmentation andreordering, multiplexing between logical and transport channels, andradio resource allocations to the UE 650 based on various prioritymetrics. The controller/processor 675 is also responsible for HARQoperations, retransmission of lost packets, and signaling to the UE 650.

The TX processor 616 implements various signal processing functions forthe L1 layer (i.e., physical layer). The signal processing functionsincludes coding and interleaving to facilitate forward error correction(FEC) at the UE 650 and mapping to signal constellations based onvarious modulation schemes (e.g., binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK),M-quadrature amplitude modulation (M-QAM)). The coded and modulatedsymbols are then split into parallel streams. Each stream is then mappedto an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot)in the time and/or frequency domain, and then combined together using anInverse Fast Fourier Transform (IFFT) to produce a physical channelcarrying a time domain OFDM symbol stream. The OFDM stream is spatiallyprecoded to produce multiple spatial streams. Channel estimates from achannel estimator 674 may be used to determine the coding and modulationscheme, as well as for spatial processing. The channel estimate may bederived from a reference signal and/or channel condition feedbacktransmitted by the UE 650. Each spatial stream is then provided to adifferent antenna 620 via a separate transmitter 618TX. Each transmitter618TX modulates an RF carrier with a respective spatial stream fortransmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to thereceiver (RX) processor 656. The RX processor 656 implements varioussignal processing functions of the L1 layer. The RX processor 656performs spatial processing on the information to recover any spatialstreams destined for the UE 650. If multiple spatial streams aredestined for the UE 650, they may be combined by the RX processor 656into a single OFDM symbol stream. The RX processor 656 then converts theOFDM symbol stream from the time-domain to the frequency domain using aFast Fourier Transform (FFT). The frequency domain signal comprises aseparate OFDM symbol stream for each subcarrier of the OFDM signal. Thesymbols on each subcarrier, and the reference signal, is recovered anddemodulated by determining the most likely signal constellation pointstransmitted by the BS 610. These soft decisions may be based on channelestimates computed by the channel estimator 658. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the BS 610 on the physical channel.The data and control signals are then provided to thecontroller/processor 659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor 659 can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the BS 610, thecontroller/processor 659 implements the L2 layer for the user plane andthe control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the BS 610.The controller/processor 659 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the BS 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the BS 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters 654TX. Each transmitter 654TX modulates an RF carrier witha respective spatial stream for transmission.

The UL transmission is processed at the BS 610 in a manner similar tothat described in connection with the receiver function at the UE 650.Each receiver 618RX receives a signal through its respective antenna620. Each receiver 618RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the controller/processor 675provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

The controller/processor 659 may direct the operation at the UE 650. Thecontroller/processor 659 and/or other processors, components, and/ormodules at the UE 650 may perform or direct operations performed by theUE as described herein. The controller/processor 675 may direct theoperations at the BS 610. The controller/processor 675 and/or otherprocessors, components, and/or modules at the BS 610 may perform ordirect operations performed by the BS as described herein. In aspects,one or more of any of the components shown in FIG. 6 may be employed toperform example operations 1300, 1400, 1700, and 1800 shown in FIGS. 13,14, 17, and 18, respectively, and can also perform other UE and BSoperations for the techniques described herein.

For example, one or more of the antenna 620, transceiver 618,controller/processor, and memory 676 may be configured to receive anuplink reference signal from a UE, measure the uplink reference signal,and transmit a handover command, as described herein. One or more of theantenna 652, transceiver 654, controller/processor 659, and memory 660may be configured to transmit an uplink reference signal and receive abeamformed downlink signal or handover command, as described herein.

Example NR/5G RAN Architecture

While aspects of the examples described herein may be associated withLTE technologies, aspects of the present disclosure may be applicablewith other wireless communications systems, such as NR or 5Gtechnologies.

New radio (NR) may refer to radios configured to operate according to anew air interface (e.g., other than Orthogonal Frequency DivisionalMultiple Access (OFDMA)-based air interfaces) or fixed transport layer(e.g., other than Internet Protocol (IP)). NR may utilize OFDM with a CPon the uplink and downlink and include support for half-duplex operationusing TDD. NR may include Enhanced Mobile Broadband (eMBB) servicetargeting wide bandwidth (e.g. 80 MHz beyond), millimeter wave (mmW)targeting high carrier frequency (e.g. 60 GHz), massive MTC (mMTC)targeting non-backward compatible MTC techniques, and/or missioncritical targeting ultra reliable low latency communications (URLLC)service.

A single component carrier bandwidth of 100 MHZ may be supported. NRresource blocks may span 12 sub-carriers with a sub-carrier bandwidth of75 kHz over a 0.1 ms duration. Each radio frame may consist of 50subframes with a length of 10 ms. Consequently, each subframe may have alength of 0.2 ms. Each subframe may indicate a link direction (i.e., DLor UL) for data transmission and the link direction for each subframemay be dynamically switched. Each subframe may include DL/UL data aswell as DL/UL control data. UL and DL subframes for NR may be asdescribed in more detail below with respect to FIGS. 9 and 10.

Beamforming may be supported and beam direction may be dynamicallyconfigured. MIMO transmissions with precoding may also be supported.MIMO configurations in the DL may support up to 8 transmit antennas withmulti-layer DL transmissions up to 8 streams and up to 2 streams per UE.Multi-layer transmissions with up to 2 streams per UE may be supported.Aggregation of multiple cells may be supported with up to 8 servingcells. Alternatively, NR may support a different air interface, otherthan an OFDM-based interface. NR networks may include entities suchcentral units or distributed units

The RAN may include a central unit (CU) and distributed units (DUs). ANR BS (e.g., gNB, 5G Node B, Node B, transmission reception point (TRP),access point (AP)) may correspond to one or multiple BSs. NR cells canbe configured as access cells (ACells) or data only cells (DCells). Forexample, the RAN (e.g., a central unit or distributed unit) canconfigure the cells. DCells may be cells used for carrier aggregation ordual connectivity and may not be used for initial access, cellselection/reselection, or handover. In some cases DCells may nottransmit synchronization signals (SS)—in some case cases DCells maytransmit SS. NR BSs may transmit downlink signals to UEs indicating thecell type. Based on the cell type indication, the UE may communicatewith the NR BS. For example, the UE may determine NR BSs to consider forcell selection, access, handover, and/or measurement based on theindicated cell type.

FIG. 7 illustrates an example logical architecture of a distributed RAN700, according to aspects of the present disclosure. A 5G access node706 may include an access node controller (ANC) 702. The ANC may be acentral unit (CU) of the distributed RAN 700. The backhaul interface tothe next generation core network (NG-CN) 704 may terminate at the ANC.The backhaul interface to neighboring next generation access nodes(NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs708 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs,or some other term). As described above, a TRP may be usedinterchangeably with “cell.”

The TRPs 708 may be a distributed unit (DU). The TRPs may be connectedto one ANC (ANC 702) or more than one ANC (not illustrated). Forexample, for RAN sharing, radio as a service (RaaS), and servicespecific AND deployments, the TRP may be connected to more than one ANC.A TRP may include one or more antenna ports. The TRPs may be configuredto individually (e.g., dynamic selection) or jointly (e.g., jointtransmission) serve traffic to a UE.

The local architecture 700 may be used to illustrate fronthauldefinition. The architecture may be defined that support fronthaulingsolutions across different deployment types. For example, thearchitecture may be based on transmit network capabilities (e.g.,bandwidth, latency, and/or jitter).

The architecture may share features and/or components with LTE.According to aspects, the next generation AN (NG-AN) 710 may supportdual connectivity with NR. The NG-AN may share a common fronthaul forLTE and NR.

The architecture may enable cooperation between and among TRPs 708. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 702. According to aspects, no inter-TRP interface may beneeded/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture 700. The PDCP, RLC, MAC protocolmay be adaptably placed at the ANC or TRP.

According to certain aspects, a BS may include a central unit (CU)(e.g., ANC 702) and/or one or more distributed units (e.g., one or moreTRPs 708).

FIG. 8 illustrates an example physical architecture of a distributed RAN800, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 802 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU) 804 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge.

A distributed unit (DU) 706 may host one or more TRPs. The DU may belocated at edges of the network with radio frequency (RF) functionality.

FIG. 9 is a diagram 900 showing an example of a DL-centric subframe. TheDL-centric subframe may include a control portion 902. The controlportion 902 may exist in the initial or beginning portion of theDL-centric subframe. The control portion 902 may include variousscheduling information and/or control information corresponding tovarious portions of the DL-centric subframe. In some configurations, thecontrol portion 902 may be a physical DL control channel (PDCCH), asindicated in FIG. 9. The DL-centric subframe may also include a DL dataportion 904. The DL data portion 904 may sometimes be referred to as thepayload of the DL-centric subframe. The DL data portion 904 may includethe communication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion 904 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include a common UL portion 906. Thecommon UL portion 906 may sometimes be referred to as an UL burst, acommon UL burst, and/or various other suitable terms. The common ULportion 906 may include feedback information corresponding to variousother portions of the DL-centric subframe. For example, the common ULportion 906 may include feedback information corresponding to thecontrol portion 902. Non-limiting examples of feedback information mayinclude an ACK signal, a NACK signal, a HARQ indicator, and/or variousother suitable types of information. The common UL portion 906 mayinclude additional or alternative information, such as informationpertaining to random access channel (RACH) procedures, schedulingrequests (SRs), and various other suitable types of information. Asillustrated in FIG. 9, the end of the DL data portion 904 may beseparated in time from the beginning of the common UL portion 906. Thistime separation may sometimes be referred to as a gap, a guard period, aguard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the subordinate entity (e.g., UE)) to UL communication(e.g., transmission by the subordinate entity (e.g., UE)). One ofordinary skill in the art will understand that the foregoing is merelyone example of a DL-centric subframe and alternative structures havingsimilar features may exist without necessarily deviating from theaspects described herein.

FIG. 10 is a diagram 1000 showing an example of an UL-centric subframe.The UL-centric subframe may include a control portion 1002. The controlportion 1002 may exist in the initial or beginning portion of theUL-centric subframe. The control portion 1002 in FIG. 10 may be similarto the control portion 1002 described above with reference to FIG. 9.The UL-centric subframe may also include an UL data portion 1004. The ULdata portion 1004 may sometimes be referred to as the payload of theUL-centric subframe. The UL portion may refer to the communicationresources utilized to communicate UL data from the subordinate entity(e.g., UE) to the scheduling entity (e.g., UE or BS). In someconfigurations, the control portion 1002 may be a physical UL sharedchannel (PUSCH).

As illustrated in FIG. 10, the end of the control portion 1002 may beseparated in time from the beginning of the UL data portion 1004. Thistime separation may sometimes be referred to as a gap, guard period,guard interval, and/or various other suitable terms. This separationprovides time for the switch-over from DL communication (e.g., receptionoperation by the scheduling entity) to UL communication (e.g.,transmission by the scheduling entity). The UL-centric subframe may alsoinclude a common UL portion 1006. The common UL portion 1006 in FIG. 10may be similar to the common UL portion 1006 described above withreference to FIG. 10. The common UL portion 1006 may additional oralternative include information pertaining to channel quality indicator(CQI), sounding reference signals (SRSs), and various other suitabletypes of information. One of ordinary skill in the art will understandthat the foregoing is merely one example of an UL-centric subframe andalternative structures having similar features may exist withoutnecessarily deviating from the aspects described herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE₁) to anothersubordinate entity (e.g., UE₂) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum)

Example Downlink-Based Mobility Procedure

FIG. 11 illustrates an example call-flow diagram illustrating operations1100 which may be performed in a handover procedure, according tocertain wireless technologies. For example, in a 4G communicationsystem, a UE 1102 synchronizes to a source BS 1104. At 1108, the sourceBS 1104 provides (e.g., transmits) a measurement configuration to the UE1102. The measurement configuration may include one or more of the cellson which the UE 1102 may perform measurements, criteria used by the UE1102 to trigger a transmission of a measurement report, and/or themeasurements that the UE 1102 may perform.

At 710, the UE 1102 measures downlink signals transmitted by a target BS1106 according to the received measurement configuration. For example,the UE 1102 may measure cell specific reference signals (CRS)transmitted by the target BS 706 in an effort to determine downlinkchannel quality. A handover trigger 1112 occurs based, at least in part,on the UE downlink signal measurements. For example, the handovertrigger at 1112 may occur upon determining the downlink channel qualityassociated with the target BS 1106 exceeds the downlink channel qualityassociated with the source BS 1104.

In response to the handover trigger, at 1114, the UE 1102 transmits astatus request (SR) message to the source BS 1104. The source BS 114transmits an uplink allocation at 1116 to the UE 1102. The UE 1102transmits a measurement report at 1118 using the received uplinkallocation. At 1120, the source BS 1104 and target BS 1106 exchangeinformation and make a handover decision regarding the UE 1102 based onthe received measurement report. Accordingly, the handover decision maybe based, at least in part, on downlink signal measurements taken by theUE 1102.

Based on the handover decision at 1120, the source BS 1104 transmits, at1122, a radio resource control (RRC) connection reconfiguration message,indicating a request to modify an RRC connection and perform a handoverto the target BS 1106. After receiving the handover command, the UE1102, at 1124, performs a random access procedure with the target BS1106. At 1126, the UE 1102 receives a random access response and uplinkallocation from the target BS 1106. At 1128, the UE 1102 transmits anRRC connection reconfiguration complete message to the target BS 1106,confirming completion of the RRC connection reconfiguration.

Example Uplink-Based Mobility

As described above, handover decisions may be based on measurements ofreceived downlink signals (e.g., downlink-based mobility). In an effortto perform handovers in a user-centric environment, it may be desirableto perform handovers based, at least in part, on uplink signalmeasurements taken by BSs. For example, NR/5G and other futurecommunication systems may focus on creating a more user-centric network.User-centric networking may refer the use of user devices in autonomicand self-organizing wireless community networks, for example, createdand controlled by the user.

FIG. 12 is an example call-flow diagram illustrating operations 1200which may be performed in a handover procedure, according to certainaspects of the present disclosure. At 1208, the source BS 1204 providesthe UE 1202 with a configuration for an uplink reference signal to betransmitted by the UE 1202. This uplink reference signal, which may bereferred to as a “chirp”, may be advantageously received by both thesource BS 1204 and one or more target BS 1206.

Although not shown in FIG. 12, the source BS 1204 and target BS 1206 mayexchange information regarding the UE 1202 (e.g., via an X2 interface orbackhaul connection), in an effort to facilitate the target BS 1206detecting the uplink reference signal. For example, the target BS 1206may receive a UE ID and/or reference signal configuration (e.g., chirpconfiguration) from the source BS 1204. In this manner, the target BS1206 may be aware of the UE 1202 and may detect the uplink referencesignal.

According to certain aspects, though not illustrated in FIG. 12, powercontrol commands may be received by the UE 1202 for the uplink referencesignal. For example, the source BS 1204 may transmit power controlcommands for the uplink reference signal in an effort for the target BS1206 to receive the uplink reference signal.

According to certain aspects, the uplink reference signal may include acyclic prefix (CP) configuration which may assist the target BS 1206 indetecting the chirp signal. Since uplink signals may be time-alignedwith the source BS 1204, allowing a special CP configuration for thechirp signal may increase chances of reception by the target BS.

As compared to the handover procedure illustrated in FIG. 11, aspectsdescribed herein allow a handover decision to be made based on uplinkreference signal measurements taken by the source BS 1204 and the targetBS 1206. In this manner, as will be described with reference to FIG. 12,the UE 1202 receives a “keep alive” (KA)/handover command or a RRCconnection reconfiguration message from the target BS 1206, as opposedto receiving the RRC connection reconfiguration message from the sourceBS 1204.

At 1210, the UE 1202 transmits an uplink reference signal, in accordancewith the received chirp configuration, capable of being received by boththe source BS 1204 and the target BS 1206. The source BS 1204 and thetarget BS 1206 measure the received uplink reference signal. At 1212,the source BS 1204 and the target BS 1206 may collectively decide tohandover the UE 1202 from the source BS 1204 to the target BS 1206 basedon uplink measurements of the chirp signal.

At 1214, either the source BS 1204 or the target BS 1206 may transmit aKA/handover command to the UE 1202, indicating a handover is to beperformed. According to certain aspects, the KA/handover message may bescrambled by a UE identifier, as opposed to, for example, a cellidentification. Scrambling by the UE identifier enables the target BS1206 to transmit the KA/handover command at 1214. The KA/handovermessage may include the target BS's cell identification and timingadvance (TA). According to certain aspects, the target BS 1206 maydetermine the TA based on the received uplink reference signal.Additionally, the KA/handover command 1214 may include anuplink/downlink allocation for the target BS 1206 and UE 1202. In thismanner, the UE 1202 may begin communicating with the target BS 1206after receiving the KA/handover command.

At 1216, at least one of the source BS 1204 or the target BS 1206 maytransmit an RRC connection reconfiguration message indicating a requestto modify an RRC connection. For example, the BS which initiates thehandover may transmit the RRC connection reconfiguration message. At1218, the UE 1202 transmits an RRC connection reconfiguration completemessage to the target BS 1206.

As described above, an uplink reference signal transmitted by the UE1202 allows the source BS 1204 and one or more potential target BS 1206to measure uplink signal strength. The uplink reference signal may be anRRC dedicated uplink reference signal. According to aspects, the uplinkreference signal may be an uplink wide-band signal.

FIG. 13 illustrates example operations 1300 which may be performed by aUE (e.g., UE 110), according to aspects of the present disclosure. Theoperations may be performed by one or more components of UE 650illustrated in FIG. 6. For example, one or more of the antenna 652,transceiver 654, controller/processor 659, and memory 660 may beconfigured to perform the operations illustrated in FIG. 13.

At 1302, the UE may be configured to transmit an uplink referencesignal. At 1304, the UE may be configured to receive a handover commandbased, at least in part, on the uplink reference signal. At 1306, the UEmay be configured to take one or more actions to perform a handover to atarget BS in accordance with the handover command.

As described above, the UE may receive a configuration for the uplinkreference signal from a serving BS, wherein the configuration allows thetarget BS to receive the uplink reference signal. Advantageously, thehandover command may be received from a serving BS or a target BS. Thehandover command may be scrambled by a UE identifier (as opposed to acell ID). Similar to the handover command, a connection reconfigurationmessage may be received from one of the serving BS or the target BS.

The handover command may include one or more of a cell identificationassociated with a target BS, a timing advance (TA) associated with thetarget BS, or an uplink/downlink resource allocation for communicatingwith the target BS.

The UE may receive a power control command from the serving BS for theuplink reference signal and may transmit the uplink reference signal inaccordance with received power control command.

As described above, a cyclic prefix (CP) of the uplink reference signalmay be longer than a CP is longer than a CP of another type of referencesignal, in an effort to assist the target BS to detect the uplinkreference signal.

FIG. 14 illustrates example operations 1400 which may be performed by afirst BS, such as a BS serving a UE or a non-serving BS, according toaspects of the present disclosure. The operations may be performed byone or more components of BS 610 illustrated in FIG. 6. For example, oneor more of the antenna 620, transceiver 618, controller/processor 675,and memory 676 may be configured to perform the operations 1400.

At 1402, the BS may receive an uplink reference signal from a userequipment (UE). At 1404, the BS may measure the uplink reference signal.At 1406, the BS may transmit a handover command to the UE based, atleast in part, on the measured uplink reference signal.

The serving BS may transmit, to the UE, a configuration for the uplinkreference signal, wherein the configuration allows a second, non-servingBS to receive the uplink reference signal.

A non-serving BS (e.g., a target BS) may receive, from the serving BS, aconfiguration for the uplink reference signal, wherein the configurationallows the non-serving BS to receive the uplink reference signal.

As described above, either the serving or non-serving BS may transmit aconnection reconfiguration message to the UE.

Aspects described herein allow support for forward and backward handoverusing an uplink reference signal. For example, a forward handover mayrefer to a handover where a UE receives the handover command directlyfrom a target BS. According to one example of a forward handover, withreference to FIG. 1, a UE 110 communicating with a source BS 132 mayhandover to a target BS 122 without the source BS 132 first preparingthe target BS 122 for the handover. A backward handover may refer to ahandover wherein the UE receives a handover command from the serving BS.By using an uplink signal which may be received by a serving andnon-serving BS, aspects of the present disclosure allow handoverdecisions to be made using measurement of the uplink reference signal.

Example Beam Selection for Uplink and Downlink Based Mobility

In some cases, advanced radio-access technology (RAT) networks (e.g., 5Gsystems and beyond) may be deployed with multiple base stations (BSs)(e.g., transmission reception Points (TRPs), gNBs, new radio (NR) BSs,access points (APs), Node Bs (NBs), 5G NBs, etc.), for example, such asBS 122. In such cases, data may be beamformed via the BSs.

In such advanced RAT networks, there may be two general types ofmobility procedures: uplink-based and downlink-based mobilityprocedures. For the uplink based case, a UE (e.g., UE 110) may send anuplink reference signal (e.g., such as the UE chirp, described hereinand also referred to as an uplink synchronization signal (USS), uplinkmobility indication channel (UMICH), or uplink reference signal (URS))and the network (e.g., BS) may measure the uplink reference signals andmake a mobility decision based on the measurement. On the other hand,for the downlink-based case, the network sends downlink referencesignals (e.g., measurement reference signals (MRS)) and UE measures thedownlink reference signals and sends a measurement report messageincluding the measured results of the downlink reference signals whencertain reporting criteria are met.

Aspects of the present disclosure provide mechanisms for beam basedwireless communication systems that may help efficiently perform a beamselection with UL based techniques, DL based techniques, or a “hybrid”combination of both UL and DL based techniques.

Beam-based mobility procedures (e.g., to select different beams based onchannel conditions) may be implemented using a variant of existingmobility procedures, but repeated with (reference signals transmittedusing) different beams. For example, starting from primarysynchronization signal (PSS) and/or secondary synchronization signal(SSS) to subsequent signals based on transmit/receive (Tx/Rx) beampairs.

Aspects of the present disclosure provide a beam selection mechanism forsuch RAT networks for downlink-based, uplink-based, and hybriduplink-downlink-based mobility scenarios.

Example Beam Selection for Uplink-Based Mobility

For UL based mobility (which may also be referred to as UE-CentricMobility as it is based on UL reference signals transmitted by a UE),design targets may be reduced network RS transmission for energy saving,improved handover reliability, reduced handover frequency, and improvedUE power saving.

FIG. 15 is an example state diagram illustrating example UE-centricuplink-based mobility, in accordance with the disclosure. As illustratedin FIG. 15, the UE (e.g., UE 110) can perform an initial connectionprocedure at 1502-1514. The UE may be in an RRC_IDLE state during theinitial access. In the RRC_IDLE state, the UE may have no dedicatedresources. The UE may monitor a paging channel with a long discontinuousreception (DRX) cycle (e.g., around 320 ms-2560 ms). The UE can receivemultimedia broadcast multicast service (MBMS) data while in this state.Cell selection can be performed for the initial access.

As shown in FIG. 15, at 1502, the UE monitors the synchronizationchannel found during cell selection, for example, for a primarysynchronization signal (PSS) or secondary SS (SSS). Once the UE issynchronized, the UE can receive physical broadcast channel (PBCH) andsystem information (SI) at 1504. At 1506, the UE sends an uplinkreference signal (e.g., chirp) and, at 1508, receives a “keep alive”(KA). The KA can indicate whether the network has data for the UE (e.g.,paging indicator=TRUE or FALSE). At 1510, the UE may receive connectionsetup information, for example, which may include the information todecode dedicated channel information, such as cell-ID, C-RNTI, timingadvance (TA) information and/or resource allocation (RA) information forthe UE. The UE can use the allocated resources to transmit an RRCconnection request message at 1512. At 1514, the UE can receive the RRCconnection setup from the BS. This may complete initial access and theUE may enter the RRC dedicated state, which may also be referred to asthe RRC_CONNECTED mode.

In the RRC dedicated state, the UE may perform the steps 1516-1522illustrated in FIG. 15. In RRC dedicated state, the UE may have C-RNTIand dedicated resources. In the RRC dedicated state, for networkcontrolled mobility, the UE monitors KA signals (e.g., a physical layer(PHY) signal) with a short DRX cycle (e.g., 2 ms-640 ms), sends uplinkreference signals (and also CQI), and uses a TA. The resource for theuplink reference signal may be UE specific resource (e.g., similar tosounding reference signal) assigned by the BS. As shown in FIG. 15, at1516, the UE receives radio resource management (RRM) configurationinformation from the BS. The RRM configuration information may relate toa mobility configuration for the UE. At 1518, the UE sends the uplinkreference signal according to the RRM configuration information. At1520, the UE monitors for the KA signal. If the KA signal indicates datafor the UE, the UE monitors the downlink channel. At 1522, the UE mayreceive a handover command in the downlink channel. In this case, the UEremains in the RRC dedicated state and may repeat the steps 1516-1522with the new (e.g., target) BS after the handover. On the other hand, ifthe KA signal does not indicate paging for the UE (e.g., after a periodof inactivity), then the UE may receive a state transition command at1524 and transition to the RRC common state. The RRC common state mayalso be referred to as the RRC inactive state, the RRC DORMANT state, orthe Energy Conserved Operation (ECO) state. The RRC common or RRCinactive state may be a substrate of the RRC_CONNECTED state or of theRRC_IDLE suspend mode. The terms may be used interchangeably.

In the RRC common state or RRC inactive state, the UE may perform thesteps 1526-1532 illustrated in FIG. 15. In the RRC common state, the UEmay have RRC common radio network temporary identifier (RC-RNTI, e.g.,Z-RNTI or C-RNTI) and common resources (e.g., rather than dedicatedresources). In the RRC common state the network can control serving nodechanges. As shown in FIG. 15, at 1526, the UE monitors forsynchronization and, at 1528 sends an uplink reference signal. Theuplink reference signal may include a UE-ID and/or a buffer statusreport (BSR) of the UE. The UE may stay in the RRC common state until itreceives a KA signal, at 1530, that indicates activity for the user (orthe UE has data to transmit), at which time the UE may performconnection setup at 1532 to transition to the RRC_CONNECTED state. Asillustrated, in RRC common state, the uplink reference signal may beused to make serving node change decisions. For example, the KA signalmay indicate the paging indication and the UE may repeat the steps1526-1530 until the KA signal indicates user plane activity for the UE.If serving cell change takes place, the network may autonomously changethe serving cell without indicating paging indicator=TRUE for the HOcommand.

According to certain aspects, for uplink-based mobility, the handoverdecision (transmission point selection) by the BS may be based onmeasurement of the uplink reference signal from the UE. For uplink-basedmobility, the BS may not send measurement reference signals (MRS) to theUE. Beam selection may also be performed by the BS based on the uplinkreference signal from the UE.

FIG. 16 is an example call flow diagram 1600 illustrating beam selectionfor uplink-based mobility, in accordance with aspects of the presentdisclosure. The call flow 1600 is more generalized version of the statediagram shown in FIG. 15 for uplink-based mobility, and also shows thebeam selection (not shown in FIG. 15). As shown in FIG. 16, at 1606, theUE 1602 can monitor synchronization signals for acquisition (e.g., shownin FIG. 15). The synchronization signals may include PSS, SSS, and/orzone SS (ZSS). At 1608, the UE 1602 sends uplink reference signals whichmay optionally include UE_ID. The uplink reference signals may besimilar to Msg 1 and Msg 3 signaling of a random access (RA) procedurein the LTE system. At 1610, the UE 1602 receives a KA signal (e.g., withPI=TRUE) from the BS 1604. Optionally, 1610 a, after receiving the KAsignal, the UE 1602 receives a Physical Cell Identity Channel (PCICH)indicting a cell-ID. At 1612, the UE 1602 receives C-RNTI, timingadvance (TA) and/or uplink grant from the BS 1604. This may be similarto Msg 2 and Msg 4 of the RA procedure. At 1615, the UE 1602 and BS 1604can exchange addition signaling similar to the conventional LTEsignaling performed after Msg 4 (e.g., completion of the RA procedure)and information configuring the uplink reference signal.

At 1616, the UE 1602 can transmit uplink reference signal(s) to the BS1604. The BS 1604 can measure the uplink reference signal(s) from the UE1602 and, at 1618, select the downlink beam and/or BS based on themeasurements. At 1620, the UE 1602 and BS 1604 can transmit uplinkand/or downlink data. In addition, channel state feedback (CSF) can betransmitted.

Example Beam Selection for Downlink-Based Mobility

FIG. 17 illustrates example operations 1700 for beam selection fordownlink-based mobility, in accordance with certain aspects of thedisclosure. The operations 1700 may be performed by a UE (e.g., UE 110).The operations 1700 may be performed by one or more components of UE 650illustrated in FIG. 6. For example, one or more of the antenna 652,transceiver 654, controller/processor 659, and memory 660 may beconfigured to perform the operations 1700.

At 1702, the UE transmits an uplink reference signal with an indicationof a preferred downlink beam. The uplink reference signal may include aUE ID. In some cases, the preferred beam may be selected (and the uplinkreference signal transmitted) during a connection establishmentprocedure. Alternatively, the uplink reference signal with the preferredbeam may be transmitted after completion of the connection establishmentprocedure. The selection of the preferred beam may be based on MRSsreceived from the BS.

At 1704, the UE receives a downlink transmission based, at least inpart, on the uplink reference signal. For example, the UE can receivebeamformed downlink transmissions based on the preferred beam or the UEcan receive a handover command based on the uplink reference signal.

FIG. 18 illustrates example operations 1800 for beam selection fordownlink-based mobility, according to aspects of the present disclosure.The operations 1800 may be performed by a BS such as BS 122. Theoperations 1800 may be performed by one or more components of BS 610illustrated in FIG. 6. For example, one or more of the antenna 620,transceiver 618, controller/processor 675, and memory 676 may beconfigured to perform the operations 1800. The operations 1800 may becomplementary operations performed by the BS to the operations 1700performed by the UE.

At 1802, the BS receives an uplink reference signal with an indicationof a preferred downlink beam. At 1804, the BS transmits a downlinktransmission based, at least in part, on the uplink reference signal.

FIGS. 19 and 20 illustrate example call flow diagrams for beam selectionfor downlink-based mobility. For DL-based mobility, the network relieson feedback provided from the UE after measuring MRS (measurementreference signals). In some cases, the MRS may be transmitted usingdifferent beams, such that the feedback is used to select a preferredbeam for DL transmissions. According to certain aspects, in an inter-BSbeam management scheme, multiple different beams may be transmitted bymultiple different BSs.

Example Beam Selection During Initial Access

According to certain aspects, the UE can send an uplink reference signalwith an indication of preferred downlink beam (e.g., or an index ofsuitable downlink beams) during initial access. For example, the uplinkreference signal can be in the first message sent from the UE to the BS.

As shown in FIG. 19, at 1906, the UE 1902 can monitor synchronizationsignals for acquisition. For downlink-based mobility case, at 1908, theBS 1904 sends reference signals (e.g., MRS) to the UE 1902. In theexample illustrated in FIG. 19, the MRS are sent during initial access.The MRS may use different beams, such that the UE 1902 can measure theMRS and select a preferred beam and/or a preferred BS, at 1910. In somecases, the UE 1502 may receive the MRS using different beamforming frommultiple BSs Then, at 1912, during the initial access (e.g., in thefirst message from the UE 1902 to the BS 1904), the UE 1902 sends anuplink reference signal with an indication of the preferred downlinkbeam and/or BS. In some cases, the indication of the preferred beam maybe an index of suitable downlink beams. The uplink reference signal mayoptionally include UE_ID.

At 1914, the UE 1902 receives a KA signal (e.g., with PI=TRUE) from theBS 1904. Optionally, 1914 a, after receiving the KA signal, the UE 1902receives a Physical Cell Identity Channel (PCICH) indicting a cell-ID.At 1916, the UE 1902 receives C-RNTI, TA and uplink grant from the BS1904. At 1918, the UE 1902 and BS 1904 can exchange addition signalingsimilar to the conventional LTE signaling performed after Msg 4 (e.g.,completion of the RA procedure) and information configuring the uplinkreference signal. At 1920, the UE 1902 and BS 1904 can exchange uplinkand downlink data and possibly CSF. The downlink data from the BS 1904may be beamformed according to the preferred beam indicated by the UE1902. The BS 1904 can also make mobility decisions and send a handovercommand based on the uplink reference signal, such as based on theindication of the preferred beam and/or BS.

As illustrated in FIG. 19, beam selection may continue after initialconnection. At 1922, further transmissions of uplink reference signalsfrom the UE 1902 (with an indication of a preferred downlink beam and/orBS) and MRS from the BS 1904 may occur. The transmissions may beperiodic and may have different configured periodicities. The furtherMRS and uplink reference signals can be used to optimize the beamselection.

Example Beam Selection after Initial Access

According to certain aspects, the MRS measurement and beam selection maynot occur until after completion of the initial access procedure asshown in FIG. 16.

As shown in FIG. 20, the initial transmissions 2006-2014 may similar tothe transmissions at 1606-1614 for the uplink-based mobility procedureillustrated in FIG. 16. At 2006, the UE 2002 can monitor synchronizationsignals for acquisition. At 2008, the UE 2002 sends an uplink referencesignal which may optionally include UE ID—but does not include theindication of the preferred downlink beam and/or transmission receptionpoint.

At 2010, the UE 2002 receives a KA signal (e.g., with PI=TRUE) from theBS 2004. Optionally, 2010 a, after receiving the KA signal, the UE 2010receives a Physical Cell Identity Channel (PCICH) indicting a cell-ID.At 2012, the UE 2002 receives TA and uplink grant from the BS 2004. At2014, the UE 2002 and BS 2004 can exchange addition signaling similar tothe conventional LTE signaling performed after Msg 4 (e.g., completionof the RA procedure) and information configuring the uplink referencesignal.

After the initial access procedure is completed, at 2016, the BS 2004sends reference signals (e.g., MRS) to the UE 2002. In some cases,multiple BSs may send reference signals to the UE 2002. The UE 2002 canmeasure the MRS and select a preferred beam and/or a preferred BS, at2018. Then, at 2020, the UE 2002 sends an uplink reference signal withthe indication of the preferred downlink beam and/or BS.

At 2022, the UE 2002 and BS 2004 can exchange uplink and downlink dataand possibly CSF. The downlink data from the BS 2004 may be beamformedaccording to the preferred downlink beam indicated by the UE 2002. TheBS 2004 can also make mobility decisions and send a handover commandbased on the uplink reference signal, such as based on the indication ofthe preferred beam and/or BS. At 2022, further transmissions of uplinkreference signals from the UE 2002 (with an indication of a preferreddownlink beam and/or BS) and MRS from the BS 2004 may occur. Thetransmissions may be periodic and may have different configuredperiodicities. The further MRS and uplink reference signals can be usedto optimize the beam selection.

Example Beam Selection for Hybrid Uplink-Downlink-Based Mobility

According to certain aspects a hybrid uplink and downlink based mobilityand beam selection approach may be used. In the hybrid approach,transmission reception point and/or beam selection decisions can bebased on both uplink and downlink reference signals. For example,similar to uplink-based mobility, mobility (e.g., handover) decisions bythe BS can be based on the uplink reference signal. However, the beamselection can be done by the UE and included in the uplink referencesignal and based on measurement of MRS with different beams transmittedby the BS.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. Further, somesteps may be combined or omitted. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed as a means plus functionunless the element is expressly recited using the phrase “means for.”

What is claimed is:
 1. A method for wireless communication by a userequipment (UE), comprising: transmitting an uplink reference signal withan indication of a preferred downlink beam; and receiving a downlinktransmission based, at least in part, on the uplink reference signal. 2.The method of claim 1, further comprising including an ID of the UE inthe uplink reference signal.
 3. The method of claim 1, furthercomprising: selecting the preferred beam during a connectionestablishment procedure, wherein transmitting the uplink referencesignal comprises transmitting the uplink reference signal during theconnection establishment procedure.
 4. The method of claim 3, furthercomprising: receiving one or more measurement reference signals (MRSs)transmitted using different beams; and selecting the preferred beambased on the one or more MRSs.
 5. The method of claim 4, wherein:receiving the one or more MRSs comprises receiving the one or more MRSsfrom a plurality of base stations (BSs); and selecting the preferredbeam comprises the preferred beam based on.
 6. The method of claim 1,wherein: the preferred beam is selected after a connection establishmentprocedure; and the uplink reference signal is transmitted while the UEis in a connected state.
 7. The method of claim 6, further comprising:during the connection establishment procedure, transmitting anotheruplink reference signal without an indication of a preferred beam. 8.The method of claim 6, wherein: the uplink reference signal does notinclude an ID of the UE.
 9. The method of claim 1, further comprising:receiving a handover command based on the uplink reference signal.
 10. Amethod for wireless communication by a base station (BS), comprising:receiving, from a user equipment (UE), an uplink reference signal withan indication of a preferred downlink beam; and transmitting a downlinktransmission to the UE based, at least in part, on the uplink referencesignal.
 11. The method of claim 10, wherein the uplink reference signalincludes an ID of the UE.
 12. The method of claim 10, furthercomprising: performing a connection establishment procedure with the UE,wherein receiving the uplink reference signal comprises receiving thepreferred beam during the connection establishment procedure.
 13. Themethod of claim 12, further comprising: transmitting one or moremeasurement reference signals (MRSs) using different beams, and whereinthe preferred beam is based on the one or more MRSs.
 14. The method ofclaim 10, further comprising: performing a connection establishmentprocedure with the UE, wherein receiving the uplink reference signalcomprises receiving the uplink reference signal after the connectionestablishment procedure while the UE is in a connected state.
 15. Themethod of claim 14, further comprising: during the connectionestablishment procedure, receiving another uplink reference signalwithout an indication of a preferred beam.
 16. The method of claim 14,wherein: the uplink reference signal does not include an ID of the UE.17. The method of claim 10, further comprising: transmitting a handovercommand based on the uplink reference signal.
 18. The method of claim10, wherein transmitting the handover command based on the uplinkreference signal comprises transmitting the handover command based on atleast one of the indication of the preferred beam or measurement of theuplink reference signal.
 19. An apparatus for wireless communication bya user equipment (UE), comprising: at least one processor configured to:transmit an uplink reference signal with an indication of a preferreddownlink beam; and receive a downlink transmission based, at least inpart, on the uplink reference signal; and a memory coupled with the atleast one processor.
 20. The apparatus of claim 19, wherein the at leastone processor is configured to: select the preferred beam during aconnection establishment procedure; and transmit the uplink referencesignal during the connection establishment procedure.
 21. The apparatusof claim 20, wherein the at least one processor is configured to:receive one or more measurement reference signals (MRSs) transmittedusing different beams, and select the preferred beam based on the one ormore MRSs.
 22. The apparatus of claim 20, wherein the at least oneprocessor is configured to: select the preferred beam after a connectionestablishment procedure; and transmit the uplink reference signal whilethe UE is in a connected state.
 23. The apparatus of claim 22, whereinthe at least one processor is further configured to: during theconnection establishment procedure, transmit another uplink referencesignal without an indication of a preferred beam.
 24. The apparatus ofclaim 20, wherein the at least one processor is further configured to:receive a handover command based on the uplink reference signal.
 25. Anapparatus for wireless communication by a base station (BS), comprising:at least one processor configured to: receive, from a user equipment(UE), an uplink reference signal with an indication of a preferreddownlink beam; and transmit a downlink transmission to the UE based, atleast in part, on the uplink reference signal; and a memory coupled withthe at least one processor.
 26. The apparatus of claim 25, wherein theat least one processor is configured to: perform a connectionestablishment procedure with the UE; and receive the uplink referencesignal during the connection establishment procedure.
 27. The apparatusof claim 26, wherein: the at least one processor is further configuredto transmit one or more measurement reference signals (MRSs) usingdifferent beams, and the preferred beam is selected based on the one ormore MRSs.
 28. The apparatus of claim 25, wherein the at least oneprocessor is configured to: perform a connection establishment procedurewith the UE; and receive the uplink reference signal while the UE is ina connected state.
 29. The apparatus of claim 25, wherein the at leastone processor is configured to: transmit a handover command based on theuplink reference signal.
 30. The apparatus of claim 25, wherein the atleast one processor is configured to transmit the handover command basedon at least one of the indication of the preferred beam or measurementof the uplink reference signal.